Amyloglucosidase-catalysed synthesis of curcumin-bis-α-d-glucoside—a response surface methodological study

Abstract

Response surface methodology (RSM) was employed to optimize amyloglucosidase-catalyzed synthesis of curcumin-bis-α-d-glucoside. A central composite rotatable design (CCRD) was employed involving five variables (enzyme concentration, curcumin concentration, incubation period, buffer concentration and pH) at five levels. A second-order polynomial equation with a R ² value 0.9 showed good correspondence between experimental and predicted yields. Three-dimensional surface and contour plots generated described the catalytic efficiency of amyloglucosidase under the reaction conditions employed. A maximum conversion of 35% was predicted for curcumin concentrations above 0.55 mmol at 35–60% (w/w d-glucose) amyloglucosidase concentrations. While lower (<35%) amyloglucosidase concentrations converted less, concentrations >60% could be inhibitory to curcumin. Extent of glucosylation was governed by a critical buffer (0.95–1.0 ml of 0.01 M pH 6.0) to enzyme ratio (15–45% w/w d-glucose). Experiments under optimum predicted conditions of 16.9% (w/w d-glucose) amyloglucosidase, 0.33 mmol curcumin, 120 h incubation period, 0.1 mM (1.0 ml of 0.01 M) buffer concentration at pH 7.5 gave a conversion yield of 56.3%. Validation experiments carried out under selected random conditions also showed good correspondence between experimental and predicted yields.